Distribution, Molecular Detection and Host Range of Groundnut Rosette Assistor Virus in Western Kenya

Groundnut (Arachis hypogaea L.) is an important legume in western Kenya, but yields are low and declining due to pests and diseases. Groundnut rosette disease (GRD) is the main disease causing upto 100% yield loss. Rosette is transmitted mainly by the groundnut aphid, Aphis craccivora Koch and to a lesser extent by Aphis gosypii Glover and Myzus persicae Sulzer. The disease is caused by synergistic interaction among groundnut rosette assistor virus (GRAV, genus Luteovirus), groundnut rosette virus (GRV, genus Umbravirus) and its associated satellite RNA (sat-RNA). The GRAV plays a crucial role in packaging the other two agents for vector transmission, and therefore a key factor in the spread of GRD. Limited information was available on distribution and host range of rosette disease in western Kenya. This study determined the distribution, molecular detection and host range of GRAV in western Kenya. A survey was conducted in Bungoma and Kakamega Counties during the short and long rains of 2016-2017. Symptomatic leafy samples were collected in RNAlater® stabilization solution and analyzed by RT-PCR. Host range studies were conducted at the Kenya Agricultural, Livestock and Research Organization (KALRO)-Kakamega. Five popular legumes of beans (Phaseolus vulgaris), cowpea (Vigna unguiculata), groundnut (Arachis hypogaea L.), green gram (Vigna radiata), soybean (Glycine max) and one solanaceous golden berry (Physalis peruviana L.) were planted in a 4×6 factorial design. The plants at three leaf-stage, were mechanically inoculated with GRD inoculum prepared from RT-PCR positive samples. The plants were monitored for symptom development in the screenhouse for 8 weeks. Total RNA was extracted from the leaf samples using RNeasy Mini Kit (Qiagen) according to the manufacturers’ protocol. A two-step RT-PCR was done using primers designed targeting GRAV CP gene. Rosette incidence and severity was significantly higher during the short rains than the long rains. All tested plants from the screen house developed typical GRD symptoms, and were found positive by RT-PCR. It is concluded that GRD is the major virus disease of groundnuts and infects most legumes grown in western Kenya. Breeding for resistance to both the groundnut aphid and GRAV coat protein (CP) gene, might be the only practical solution.